Extractive oxidation used as a naphtha treating process is well-known, for example, the sweetening naphtha process, typically comprising a catalytic oxidation via O2 in the presence of NaOH or KOH of odor-generating mercaptans of certain raw naphthas, more specifically those from fluid catalytic cracking. See U.S. Pat. No. 2,591,946 where is taught a sweetening process for sour oils whereby mercaptans are removed from said oils by carrying out a reaction the catalyst of which is KOH, O2 and 0.004 to 0.1 wt % copper oxide based on the KOH solution.
Also, an article in the Oil and Gas Journal vol. 57(44) p.73-78 (1959) entitled. “Low Cost Way to Treat High-Mercaptan Gasoline”. by K. M. Brown et al, is directed to the discussion of the Merox process and other prior art procedures.
However, such state-of-the-art processes do not apply to raw naphtha where the target substances are those containing unsaturations and nitrogen functionalities, chiefly dienes and substances having nitrogen functionalities of a basic character, which not only cause odor but also naphtha instability caused by color as well as turbitidy caused by gums, without mentioning that such basic nitrogen compounds are harmful to the hydrodesulfurization processes used in the naphtha finishing processes that precede commercialization.
The peroxide-aided oxidation is a promising path for the refining of fossil oils, and may be directed to several goals, for example to the removal of sulfur and nitrogen compounds present in fossil hydrocarbon streams, mainly those used as fuels for which the international specification for sulfur content becomes more and more stringent.
One further application is the withdrawal of said compounds from streams used in processes such as hydrotreatment, where the catalyst may be deactivated by the high contents in nitrogen compounds.
Basically, the peroxide oxidation converts the sulfur and nitrogen impurities into higher polarity compounds, those having a higher affinity for polar solvents relatively immiscible with the hydrocarbons contaminated by the sulfur and nitrogen compounds. In this way, the treatment itself comprises an oxidation reaction step followed by a separation step of the oxidized products by polar solvent extraction and/or adsorption and/or distillation.
The oxidation reaction step using peroxides, as well as the separation steps of the oxidized compounds from the hydrocarbons have been the object of various researches.
Thus, published European Application EP0565324A1 teaches a technique exclusively focused on the withdrawal of organic sulfur from petroleum, oil shale or coal having an oxidation reaction step with an oxidizing agent like H2O2 initially at 30° C. and then heated at 50° C. in the presence of an organic acid (for example HCOOH or AcOH) dispensing with catalysts, followed by (a) a solvent extracton step, such as, N′-dimethyl formamide, dimethylsulfoxide, N,N′-dimethylacetamide, N-methylpyrrolidone, acetonitrile, trialkylphosphates, methyl alcohol, nitromethane among others; or by (b) an adsorption step with alumina or silica gel, or c) a distillation step where the improved separation yields are caused by the increase in boiling point of the sulfur oxidized compounds.
A similar treatment concept is used by D. Chapados et al in “Desulfurization by Selective Oxidation and Extraction of Sulfur-Containing Compounds to Economically Achieve Ultra-Low Proposed Diesel Fuel Sulfur Requirements”, NPRA 2000 Annual Meeting, Mar. 26-28, 2000, San Antonio, Tex., Paper AM-00-25 directed to a refining process also focused on the reduction of the sulfur content in oils, the oxidation step occurring at temperatures below 100° C. and atmospheric pressures, followed by a polar solvent extraction step and by an adsorption step. The authors further suggest the use of a solvent recovery unit and another one for the biological treatment of the concentrate (extracted oxidized products) from the solvent recovery unit, this unit converting said extracted oxidized products into hydrocarbons.
According to the cited reference by Chapados et al., the reaction phase consists of an oxidation where a polarized —O—OH moiety of a peracid intermediate formed from the reaction of hydrogen peroxide and an organic acid performs an electrophilic oxidation of the sulfur compounds, basically sulfides such as benzothiophenes and dibenzothiophenes and their alkyl-related compounds so as to produce sulfoxides and sulfones.
U.S. Pat. No. 3,847,800 teaches that the oxidation of nitrogen compounds, such as the quinolines and their alkyl-related compounds so as to produce N-oxides (or nitrones) can be promoted as well when reacting these compounds with a nitrogen oxide.
According to U.S. Pat. No. 2,804,473, the oxidation of amines with an organic peracid leads to N-oxides, therefore a reaction pathway analogous to that of sulfur-containing compounds is expected for the oxidation of nitrogen-containing compounds with a peracid derived from the peroxideforganic acid couple. In addition, the same US patent teaches a process for the production of lower aliphatic peracids.
According to this publication, peracids are useful in a variety of reactions, such as oxidation of unsaturated compounds to the corresponding alkylene oxide derivatives or epoxy compounds.
It is also known that hydrogen peroxide naturally decomposes into unstable intermediates that generate O2 and H2O, such process being accelrated by light, heat and mainly by the pH of the medium.
U.S. Pat. No. 5,917,049 teaches a process for preparing dicarboxylic acids containing at least one nitrogen atom where the corresponding heterocyclic compound having a fused benzene ring containing at least one nitrogen atom is oxidized in the presence of hydrogen peroxide, a Bronsted acid and an iron compound. The preferred iron compound is iron nitrate and nitric acid is used as Bronsted acid. The reaction occurs in an aqueous medium.
Besides, U.S. Pat. No. 4,311,680 teaches a process for removing sulfur compounds such as H2S, mercaptans and disulfides contained in gaseous streams such as natural gas by directing said gaseous stream through a Fe2O3 fixed bed in the presence of a hydrogen peroxide aqueous solution.
On the other hand, several publications report the use of the Fenton's reagent exclusively directed to the removal of pollutants from municipal and industrial aqueous wastes. See the article by C. Walling, “Fenton's Reagent Revisited”, Accts. Chem. Res., Vol. 8, p. 125-131 (1975), U.S. Pat. No. 6,126,838 and U.S. Pat. No. 6,140,294 among others.
Fenton's reagent, known since 1894, is traditionally a mixture of H2O2 and ferrous ions exclusively in an aqueous medium, so as to generate the hydroxyl radical OH. The hydroxyl radical is one of the more reactive species known. The Relative Oxidation Power, (ROP) of this radical is 2.06 (based on Cl2 the ROP of which is 1.0), being higher than that of singlet oxygen (ROP=1.78)>H2O2(ROP=1.31)>HOO. (ROP=1.25)>permanganate (ROP=1.24), this rendering such radical able to react with countless compounds.
However, either due to the presence of Fe3+ or to the natural dissociation of hydrogen peroxide, secondary reactions consume or compete with the hydroxyl radical.
Such secondary reactions can be minimized by reducing the pH since the protic acidity reverts the dissociation equilibrium of H2O2 into H+ and OOH., so as to prevent the transformation of the generated OOH— into HOO., which in turn will take more H2O2 to H2O e O2 in spite of the co-generation of the desired hydroxyl radical. On the other hand, excessive pH reduction leads to the precipitation of Fe(OH)3 which catalyses the decomposition of H2O2 into O2.
Thus, it is recommended to work at pH 2.0 to 6.0, the reaction pH being afterwards adjusted to 6.1-9.0 to allow a better product separation by the flocculation of residual ferrous sulfate salts, when such salt is the source of ferrous cations of the conventional Fenton's reagent.
However, in the case of the production of free ferric cations which could consume or inhibit the generation of the hydroxyl radical those can be scavenged by complexing agents (such as for example phosphates, carbonates, EDTA, formic aldehyde, citric acid) only if such agents do not scavenge at the same time the ferrous cations also solved in aqueous medium and required for the oxidation reaction.
Active Fe sources linked to a solid matrix useful for generating hydroxyl radicals are the iron oxyhydrates crystals, FeOOH, such as goethite, used for the hexachlorobenzene oxidation found as a pollutant of subterranean water resources.
R. L. Valentine e H. C. A. Wang, in “Iron oxide Surface Catalyzed Oxidation of Quinoline by Hydrogen Peroxide”, Journal of Environmental Engineering, 124(1), 31-38 (1998), report a procedure used exclusively in aqueous effluents using aqueous suspensions of iron oxides such as ferrihydrite, a semicrystalline iron oxide and goethite, both being previously synthesized, as catalysts of the hydrogen peroxide oxidation of a water pollution model compound—quinoline, present in concentrations of nearly 10 mg/liter in an aqueous solution the features of which mime a natural water environment.
Among the iron oxides used by the authors, a suspension of crystalline goethite containing a complexing agent (for example carbonates) produced, after 41 hours reaction, higher quinoline abatement from the aqueous solution. According to the author, the complexing agent is adsorbed on the catalyst surface so as to regulate the H2O2 decomposition. The article does not mention the formed products and the Goethite employed was a pure crystalline material synthesized by aging Fe(OH)3 at 70° C. and pH=12 during 60 h.
Pure goethite such as the one utilized by Valentine et al. is hardly found in free occurrences in nature; however, it can exist as a component of certain natural ores.
U.S. Pat. No. 5,755,977 teaches a process where a contaminated fluid such as water or a gas stream containing at least one contaminant is contacted in a continuous process with a particulate goethite catalyst in a reactor in the presence of hydrogen peroxide or ozone or both to decompose the organic contaminants. It is mentioned that the particulate goethite may also be used as a natural ore form. However, the particulate goethite material actually used by the author in the Examples was a purified form purchased from commercial sources, and not the raw natural ore.
Goethite is found in nature in the so-called limonite and/or saprolite mineral clays, occurring in laterites (natural occurrences which were subjected to non-eroded weathering, i.e. by rain), such as in lateritic nickel deposits, especially those layers close by the ones enriched in nickel ores (from 5 to 10 m from the surface). Such clays constitute the so-called limonite zone (or simply limonite), where the strong natural dissolution of Si and Mg leads to high Al, Ni concentrations (0.8-1.5 weight %), also Cr and mainly Fe (40-60 weight %) as the hydrated form of FeOOH, that is, FeOOHn H2O.
The layers below the limonite zone show larger amounts of lateritic nickel and lower amounts of iron as Goethite crystals. This is the so-called saprolite zone or serpentine transition zone (25-40 weight % Fe and 1.5-1.8 weight % Ni), immediately followed by the garnierite zone (10-25 weight % Fe and 1.8-3.5 weight % Ni) that is the main source of garnierite, a raw nickel ore for industrial use.
The open literature further teaches that the crystalline iron oxyhydroxide FeOOH may assume several crystallization patterns that may be obtained as pure crystals by synthetic processes. Such patterns are: α-FeOOH (Goethite cited above), γ-FeOOH (Lepidocrocite), β-FeOOH (Akaganeite), or still δ′-FeOOH (Ferroxyhite), this latter having also magnetic properties. The most common crystallization patterns are Goethite and Lepidocrocite.
The iron oxyhydroxide crystalline form predominant in limonite is α-FeOOH, known as Goethite. The Goethite (α-FeOOH) crystallizes in non-connected layers, those being made up of a set of double polymeric ordered chains. This is different, for example, from the synthetic form Lepidocrocite (γ-FeOOH), which shows the same double ordered chain set with interconnected chains. This structural difference renders the α-FeOOH more prone to cause migration of free species among the non-connected layers.
Limonite contains 40-60 weight % iron besides lower contents of nickel, chrome, cobalt, calcium, magnesium, aluminum and silicon oxides, depending on the site of occurrence.
The limonite specific area is 40-50 m2/g. Besides being a low cost mineral, of easy pulverization and handling; its dispersion characteristics in hydrophobic mixtures of fossil hydrocarbons are excellent.
Limonite was found to be easily dispersed in fossil oils as a precursor of pyrrothite (Fe1−x S), as reported by T. Kaneko et al in “Transformation of Iron Catalyst to the Active Phase in Coal Liquefaction”, Energy and Fuels 1998, 12, 897-904 and T. Okui et al, in “Proceedings of the Intl. Symposium on the Utilization of Super-Heavy Hydrocarbon Resources (AIST-NEDO)”, Tokyo, September 2000.
This behavior is different from that of a Fe(II) salt such as ferrous sulfate or ferrous nitrate, which requires an aqueous medium to effect the formation of Fenton's reagent.
U.S. Pat. No. 6,544,409B2 of the Applicant and herein completely incorporated as reference teaches the catalytic oxidation of organic compounds in a fossil hydrophobic medium in the presence of a peracid (or a peroxide/acid couple), the oxidation reaction being catalyzed by an iron oxide such as a powdered limonite ore working as a highly dispersible source of iron, which is highly catalytically active in this petroleum medium.
Published International Application WO04/099346 (corresponding to published US Application 2004/0222134) also of the Applicant and equally fully incorporated as reference teaches a process for the extractive oxidation of sulfur and nitrogen present in huge amounts in raw hydrocarbon streams rich in heteroatomic compounds, such streams being originated either from fossil oils or from the processing of such oils, the process serving to increase the polarity of such heteroatomic compounds, the simultaneous oxidation and aqueous extraction of the resulting oxidated compounds being effected in the presence of organic acids and peracids.
Published US Application 2004/0108252 (USSN 2002 10/314963) also of the Applicant and herein completely incorporated as reference teaches a process for the upgrading of raw hydrocarbon streams rich in heteroatomic polar compounds through the extractive oxidation of sulfur, nitrogen, conjugated dienes and other unsaturated compounds from such streams, the process involving treating such streams with an oxidizing couple which is a peroxide solution/organic acid and a limonite ore, under an acidic pH, atmospheric pressure and ambient or higher temperature.
Oxidized heteroatomic compounds are extracted into the aqueous phase, while the oxidized hydrocarbon is separated from the catalyst by decanting, etc. In this way it is possible to remove 90% by mass or more of all the nitrogen compounds and up to 99.75% by mass of the basic nitrogen compounds. However, this process leads to 5 to 10 wt % losses of the treated hydrocarbon product to the aqueous phase combined to the oxidized contaminants. Such losses should therefore be minimized.
The literature mentions processes for the treatment of organic compounds of fossil oils by oxidation in the presence of peracids (or peroxides and organic acids) as treating processes for aqeuous or gaseous organic media using Fenton's reagent, and also processes using the peroxide/organic acid couple in the presence of an iron oxide such as limonite.
However no description nor suggestion could be found in the literature for an extractive oxidation process for contaminants present in fuels, such process being catalyzed by iron oxides, where heteroatomic polar compounds, conjugated dienes and other unsaturated moieties of raw hydrocarbon streams are oxidized in the presence of an aqueous slurry of a peroxide in solution/organic acid couple and a reduced goethite iron oxide, such compounds being simultaneously removed from such streams by the oxidant itself, such process being described and claimed in the present application.